class_docstr: RCNN bbox head
  
  Args:
      head (object): the head module instance, e.g., `ResNetC5`, `TwoFCHead`
      box_coder (object): `BoxCoder` instance
      nms (object): `MultiClassNMS` instance
      num_classes: number of output classes
docstr: Get the bbox head feature map.
docstr_tok: ["Get","the","bbox","head","feature","map","."]
code: def get_head_feat(self, input=None):
      """
      Get the bbox head feature map.
      """
  
      if input is not None:
          feat = self.head(input)
          if isinstance(feat, OrderedDict):
              feat = list(feat.values())[0]
          self.head_feat = feat
      return self.head_feat
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from collections import OrderedDict
  from paddle import fluid
  from paddle.fluid.param_attr import ParamAttr
  from paddle.fluid.initializer import Normal, Xavier
  from paddle.fluid.regularizer import L2Decay
  from paddle.fluid.initializer import MSRA
label_desc: Use image node_id 2 for calling the BBoxHead obj's underlying member method code with example usage: obj.get_head_feat(input) and returns: self